1. Field of the Invention
The present invention relates to an extrusion type coating head that is used for applying, for example, magnetic coating onto a support.
2. Description of the Prior Art
Conventionally, when a magnetic recording medium is produced by applying a coating solution such as magnetic coating on a support, for example, various coating methods have been adopted such as gravure, reverse, extrusion, and doctor blade coating methods.
Among them, the extrusion type coating method is, in particular, characteristic in that a very uniform thin film is obtained even if the film thickness in wet condition is 10 .mu.m or less, and suitable for a precise thin film coating. Thus, the extrusion type coating method has been noted for a very suitable coating method as a production process of a magnetic recording medium that requires a thin film coating for the purpose of high density recording. Therefore, various extrusion type coating heads used in this coating method have been proposed heretofore.
In general, basic composition of a simplest extrusion type coating head has, as shown in FIG. 11, a front edge 111 and a back edge 113 which are jointed to each other, and side plates 114, 114 which are secured at both ends of the edges 111, 113 so as to seal the both ends thereof. The back edge 113 has a concave part to form a so-called pocket 117 and a polished surface for forming a slit 118, in which the polished surface is connected to the concave part. The accuracy of opening of the tip end of the slit 118 and the accuracy of matching the slit tip end, after the assembly of the front edge 111 and the back edge 113, delicately influence the coating quality. For this reason, the coating head that has been once assembled and minutely adjusted is desired not to be separated even at the cleaning after the coating work, without removing the joint of the front edge 111 and the back edge 113.
As a method of cleaning such coating head, in the Japanese Patent Laid-open Publication No. HEI 4-281876 proposed is a cleaning method for a coating device that is to apply a coating solution to a continuously running support. The coating device has a slot from which the coating solution is extruded and has a removable spacer which is removed after the coating work for allowing cleaning means such as a brush and high pressure hose to be inserted from an end part of the coating device, and the spacer limits the width of coating.
However, it is difficult to clean the inner part of a coating head perfectly without paying attention to the inner conditions of the extrusion type coating head by a simple mechanical treatment from outside, as proposed in the Japanese Patent Laid-open Publication No. HEI 4-281876. It has become clear in particular, as a result of ardent study by the present inventor, that the adhesion of coating solution that remains in the wall surface of the pocket in an extrusion type coating head is found to be strong and difficult for being removed cleanly. It has been also found that the coating solution may sometimes remain partially in the corner of the boundary of the slit surface and the adjacent pocket surface. In this situation it has been also found that the coating solution as a stain or fouling is difficult for being removed completely.
As explained above, the coating solution that remains as a stain or fouling in the wall surface of the pocket in an extrusion type coating head is difficult for being removed completely by usual cleaning. When the coating head that remains cleaned insufficiently is mounted again in a coating device, the streak and the coating thickness fluctuation might occur in the product coating surface.
The present invention is made under such situation and aims to improve easiness of cleaning, thereby improving the rate of operation, saving labor, and preventing adverse effects such as the streak generated on the coating surface and the thickness fluctuation in the coating that might be brought by insufficient cleaning.